HEAT oven to 375°F. Place white and sweet potatoes in separate bowls. Add half each of the cream cheese and sour cream to the potatoes in each bowl; season with salt and pepper. Mash with potato masher or fork until creamy.

STIR half of the Parmesan cheese into bowl of white potatoes. Stir half of the Cheddar cheese into bowl of sweet potatoes. Alternately layer half each of the white potato mixture and sweet potato mixture in 2-L. clear glass casserole dish. Repeat layers.

BAKE 15 min.; sprinkle with remaining cheeses, continue baking 5 min. or until cheeses are melted.